CROSBY, Tex. — The operators of a chemical plant left without power by floodwaters said Thursday that two explosions rocked the facility, and they warned that more blasts could occur as rising temperatures make the compounds inside volatile and dangerous.

“A threat of additional explosion remains,” said a statement from Arkema, the French chemicals group that runs the plant, which was under about six feet of water from the relentless rains unleashed by Harvey.

The company urged residents to stay clear of a temporary evacuation zone set up Wednesday.

The risks also appear to extend beyond explosions, as noxious fumes left at least one sheriff’s deputy in need of medical treatment.

The deputy was taken to a hospital after inhaling fumes from the plant, and nine others sought medical care as a precaution, according to the Harris Country Sheriff’s Office. Arkema officials told the sheriff’s department that the smoke inhaled by the 10 deputies is believed to be “a non-toxic irritant.”

The plant in Crosby, about 25 miles northeast of Houston, manufactures organic peroxides, a family of compounds used in everything from pharmaceuticals to construction materials such as counter tops and pipes.

But the material must remain cold — otherwise it can combust. “The material naturally degrades and some types can be unstable unless refrigerated,” Arkema explained.

The facility’s coolant system and inundated backup power generators failed, according to the company: Primary power at the plant went out on Sunday, and two sources of emergency backup power were lost shortly thereafter.

At that point, Richard Rowe, chief executive of Arkema’s North American unit, warned that explosions were likely.

“We have lost critical refrigeration of the materials on site that could now explode and cause a subsequent intense fire,” Rowe said in a statement Wednesday. “The high water and lack of power leave us with no way to prevent it. We have evacuated our personnel for their own safety. The federal, state and local authorities were contacted a few days ago, and we are working very closely with them to manage this matter. They have ordered the surrounding community to be evacuated, too.”

A mandatory evacuation zone was established for a 1.5-mile radius Wednesday as the last remaining workers at the facility attempted to resolve the problem. Police cruisers and SUVs sealed off access to the plant on Highway 90, which connects Houston and Beaumont. Parts of the highway nearby were underwater.

A continuous flow of trucks, many hauling boats to participate in flood rescue efforts, approached the police barricade near the facility Wednesday afternoon only to be turned away as Crosby Volunteer Fire Department trucks crisscrossed the highway cut-through roads.

A Crosby, Tex. volunteer fireman with an evacuee in tow answers questions on road closures from bystanders near a chemical plant authorities said is going to explode. (Alex Horton/The Washington Post)

The facility, the company noted, “is in a rural area with no hospitals, schools, correctional facilities or recreational areas or industrial/commercial areas in the vicinity.” Arkema said the plant, which employs 57 people, “has never experienced flooding of this magnitude before.”

Ahead of Harvey’s arrival, “the plant made extensive preparations,” bringing extra backup generators to the facility, along with diesel-powered refrigerated tank trailers, Arkema said. But the generators were inundated by water and failed. At that point, the company said, “temperature-sensitive products” were transferred into the diesel-powered refrigerated containers.

Still, the company said Wednesday, “the most likely outcome is that, anytime between now and the next few days, the low-temperature peroxide in unrefrigerated trailers will degrade and catch fire. There is a small possibility that the organic peroxide will release into the flood waters but will not ignite and burn. In that situation, we would expect the materials to break down rapidly into hydrocarbons and alcohols.

“The flood waters could carry the hydrocarbons and alcohols off-site. While it is possible that you may see an oil sheen or smell a slight odor, we anticipate the break down products would dissipate in the water or evaporate. In the alternate, there could be a combination event involving fire and environmental release.

“Any fire will probably resemble a large gasoline fire. The fire will be explosive and intense. Smoke will be released into the atmosphere and dissipate. People should remain clear of the area.”

On Wednesday, James and Deborah Hyer sat, frustrated, in a white pickup truck with a plant water tower in view. They were waiting with their three young children for the police to clear out so they could return to their home in Dayton, about 10 miles north of the barricade.

They were out of milk and water, with local stores either closed or cleaned out of supplies.

Their newly purchased double-wide trailer on top of a hill escaped much of the floodwaters, Deborah Hyer said, but some of their friends living at the bottom experienced complete devastation.

“They lost everything,” she said. One friend of hers, a single mother of five children, lived in a house on 17-foot stilts, but the water rose so high she had to evacuate, she said.

In tiny Kenefick to the northeast, neighborhoods built on the floodplains and banks of the Trinity River were destroyed, and relatives of friends who tried to evacuate were still missing.

As in other areas like Houston and its western suburb of Katy, residents remarked on the quick response of volunteers with fishing boats fanning out as self-deputized rescue units.

“Some authorities are helping, but civilians like the Cajun Navy are helping the most,” James Hyer said.

A Crosby Volunteer Fire Department truck with flashing lights stopped as another man flagged him down to get updates on alternate routes to Dayton.

“We have nowhere to go,” James Hyer pleaded to the firefighter.

“I’d go away from here,” the firefighter responded, though he conceded he did not know which nearby back roads were flooded or, like Highway 90, sealed by police. The Hyer family, resigned, turned around with their backs to Dayton.

Cleveland Walters, Jr. waits for a police barricade to close down on Highway 90 in Crosby, Tex. Police sealed off the highway following reports of an imminent explosion at a chemical plant after floodwaters damaged its coolant systems. (Alex Horton/The Washington Post)

Cleveland Walters Jr., who also lives in Dayton, waited more than an hour outside his black GMC pickup to get home, where his wife and elderly 92-year old father needed to be cared for, he said.

“Dayton is where all my medicine is,” he said, ticking off the medical issues stemming from Agent Orange he said he was exposed to while serving in the U.S. Air Force in Guam during the final years of the Vietnam War.

The runways for B-52 Stratofortress bombers taking off were choked with jungles, and the defoliant sprayed around his tent sparked skin and gastrointestinal problems. He takes about 30 pills a day, he said, and had only a limited supply with him as he sat on Highway 90.

But Walters wasn’t overly concerned about the plant’s reported impending explosion, after working in the oil industry for many years after his service.

“I drive by it about every day. It is what it is,” he said. He left soon after, and like the Hyer family, put more distance between himself and Dayton as rescue vehicles roared to Beaumont.

du Lac reported from Washington. Steven Mufson and Brian Murphy contributed to this report, which has been updated.